Optical scanning apparatus and image forming apparatus

ABSTRACT

An optical scanning apparatus includes a polygonal mirror configured to deflect a light beam emitted from a light source such that the laser beam scans a member to be scanned, a drive motor configured to rotate the polygonal mirror, aboard on which the polygonal mirror and the drive motor are mounted, an installation portion where the board is installed, a rubber member provided between the board and the installation portion, and an adjustment unit configured to position on the board with respect to the installation portion and to adjust inclination of the board with respect to the installation portion by deforming the rubber member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/916,402 filed on Oct. 29, 2010, which claims priority to JapanesePatent Application No. 2009-272572 filed Nov. 30, 2009. Each of U.S.patent application Ser. No. 12/916,402 and Japanese Patent ApplicationNo. 2009-272572 is hereby incorporated by reference herein in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrophotographic image formingapparatus and an optical scanning apparatus which is mounted in theelectrophotographic image forming apparatus, such as a digital copyingmachine, a laser beam printer, or a facsimile apparatus, and which isadapted to perform scanning with a laser beam.

2. Description of the Related Art

Conventionally, an electrophotographic image forming apparatus containsan optical scanning apparatus having a polygonal mirror to deflect alight beam emitted from a semiconductor laser constituting a lightsource such that the light beam scans a photosensitive drum as aphotosensitive member. In an electrophotographic image formingapparatus, a light beam corresponding to image information is emittedfrom an optical scanning apparatus and applied to a photosensitive drumwhose surface is charged, and scanning is performed on thephotosensitive drum with the light beam, to form an electrostatic latentimage on the photosensitive drum. The electrostatic latent image formedon the photosensitive drum is developed with a developer. The developedimage is transferred and fixed to a recording medium such as a papersheet.

In such an optical scanning apparatus, a rotation shaft for rotating thepolygonal mirror may be inclined with respect to a desired installationangle for the rotation shaft (Hereinafter, this inclination will bereferred to as shaft inclination). The shaft inclination is aninclination caused by limitations in production precision. If thepolygonal mirror has shaft inclination, the incident position andincident angle on a scanning lens may uniformly deviate from the designvalues, which lead to a deterioration in image formation performance,such as disturbance of the light beam spot shape on the photosensitivedrum, thus resulting in degradation in image quality.

FIGS. 8A and 8B illustrate an example of a conventional configuration ofan optical scanning apparatus. FIG. 8A is a side view of a polygonalmirror and its periphery, and FIG. 8B is a perspective view of thepolygonal mirror and its periphery.

In the optical scanning apparatus illustrated in FIG. 8A, a drive motor803 for driving a polygonal mirror 804 has a bearing 802. The bearing802 is fit-engaged with a hole provided in a board 801 (hereinafterreferred to as the drive board) on which a drive circuit for driving thedrive motor 803 is mounted, whereby the drive motor 803 is mounted onthe drive board 801. Further, the bearing 802 is fit-engaged with apositioning hole 808 provided in an optical box 807 of the opticalscanning apparatus, whereby positioning is effected on the drive motor803 with respect to the optical box 807. The bearing 802 bears the shaftof the rotor portion of the drive motor 803, and a polygonal mirror 805is mounted on the rotation shaft 804 of the rotor portion. The polygonalmirror 805 is fixed to the rotor portion from above by a plate spring orthe like.

The drive board 801 is fixed to the optical box 807 by passing screwsthrough screw holes provided in bosses 809, 810, 811, and 812 andthrough optical-box-side fixation holes 813, 814, 815, and 816 and bytightening the screws.

Since the bearing 802 is mounted on the drive board 801 by swaging orthe like, there may be variations in the angle of the rotation shaft 804with respect to the drive board 801 due to the production precision ofthe members and the precision of the swaging. Further, when the driveboard 801 is formed of sheet metal, there is possibility of the driveboard 801 being warped. Then, the rotation shaft 804 on which thepolygonal mirror 805 is mounted is tilted accordingly (shaftinclination), and the reflection surface of the polygonal mirror 805 isalso inclined, and so the reflection angle in the sub-scanning directionof the reflection light may deviate from the ideal position, thusresulting in deterioration in optical characteristics.

Further, it is also difficult for the mounting bearing surface of theoptical box 807 to be machined into a flat surface in a strict sense,and this deviation from the ideal flat surface also leads to shaftinclination of the polygonal mirror.

To address these problems, Japanese Patent Application Laid-Open No.2005-201941 discusses an apparatus capable of correcting shaftinclination. The apparatus discussed in Japanese Patent ApplicationLaid-Open No. 2005-201941 is equipped with a mechanism pressing a driveboard against a bearing surface formed on an optical box via a spring tovary a screw tightening amount, thereby reducing shaft inclination.

However, in a case where the drive board is fixed to the opticalscanning apparatus via a sprig as in Japanese Patent ApplicationLaid-Open No. 2005-201941, if the reaction force of the spring is weak,the polygonal mirror cannot be firmly fixed in position with respect tothe optical scanning apparatus main body due to rotational vibrationgenerated at the time of rotation of the polygonal mirror. When thepolygonal mirror is not firmly fixed in position, the polygonal mirrorvibrates due to the vibration generated at the time of rotation of thepolygonal mirror, and, due to the influence of the vibration, there is afear of the image forming position of the laser beam on thephotosensitive drum deviating from the ideal position.

Thus, if the polygonal mirror is to be fixed to the optical box with aforce strong enough to withstand the rotational vibration, there arisesof necessity a need to secure a large spring deformation amount. Thus,to generate a large force, the size of the spring must be increased,which is an obstruction to a reduction in size of the optical scanningapparatus.

SUMMARY OF THE INVENTION

The present invention is directed to, among other things, a drive motorshaft inclination adjusting mechanism which is small and capable ofreliable adjustment.

According to an aspect of the present invention, an optical scanningapparatus includes a polygonal mirror configured to deflect a light beamemitted from a light source such that the light beam scans a member tobe scanned, a drive motor configured to rotate the polygonal mirror, aboard on which the polygonal mirror and the drive motor are mounted, aninstallation portion where the board is installed, a rubber memberprovided between the board and the installation portion, and anadjustment unit configured to position the board with respect to theinstallation portion and to adjust inclination of the board with respectto the installation portion by deforming the rubber member.

Further features and aspects of the present invention will becomeapparent from the following detailed description of exemplaryembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate exemplary embodiments, features,and aspects of the invention and, together with the description, serveto explain the principles of the invention.

FIG. 1 is a schematic sectional view of a photosensitive drum and itsperiphery in an optical scanning apparatus according to an exemplaryembodiment of the present invention.

FIG. 2 is a perspective view of the interior of an optical scanningapparatus according to an exemplary embodiment of the present invention.

FIGS. 3A and 3B are a perspective view and a plan view, respectively,illustrating a scanning unit and its periphery in an optical scanningapparatus according to an exemplary embodiment of the present invention.

FIG. 4 illustrates a fluctuation amount of a rotation shaft at the timeof shaft inclination adjustment in an exemplary embodiment of thepresent invention.

FIG. 5 illustrates the relationship between a reaction force of anO-ring and a vibration on a drive board.

FIGS. 6A to 6E are diagrams illustrating clearance portions provided todeal with compressive deformation of an O-ring.

FIG. 7 illustrates the relationship between the compression amount of anO-ring and the reaction force thereof.

FIGS. 8A and 8B are a sectional view and a perspective view,respectively, of a scanning unit and its periphery in a conventionaloptical scanning apparatus.

DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments, features, and aspects of the inventionwill be described in detail below with reference to the drawings.

FIG. 1 is a schematic sectional view of a photosensitive drum and itsperiphery in an electrophotographic copying machine employing an opticalscanning apparatus according to a first exemplary embodiment of thepresent invention. An image forming process will be described withreference to FIG. 1. A laser beam (light beam) emitted from a lightsource (not shown) deflects by a polygonal mirror 204 a (rotatingpolygonal mirror), and is guided to a photosensitive drum 101(photosensitive member as a member to be scanned by the laser beam) viavarious optical systems including a lens described below, a reflectionmirror, etc. The photosensitive drum 101 is uniformly charged by acharging device 102, and is then exposed to the laser beam emitted froma semiconductor laser (described below) of a light source unit in anoptical scanning apparatus 200 based on input image data. Thephotosensitive drum 101 rotates at a fixed speed, and the photosensitivesurface of the photosensitive drum 101 moves in a sub-scanning direction(the rotating direction of the photosensitive drum) with respect to thelight beam. In this way, an electrostatic latent image based on theimage data is formed on the photosensitive drum 101. This electrostaticlatent image is developed by toner, which is a developer retained by adeveloping device 103. After this, a bias is applied to a transferroller 104 constituting a transfer device, whereby the toner image borneby the photosensitive drum 101 is transferred to a transfer material P(a recording medium), conveyed on a conveyance path 105, at a transferportion T formed by the transfer roller 104 and the photosensitive drum101. Then, the transfer material P bearing the toner image is conveyedto a fixing device (not shown), and a fixing processing is performed onthe toner image on the transfer material P through heating, etc., toobtain a transfer material with the image formed thereon.

FIG. 2 is a perspective view of an example of the optical scanningapparatus 200 used in a laser printer, a digital copying machine or thelike forming an image by the above-described image forming process. Asillustrated in FIG. 2, the optical scanning apparatus 200 includes alight source unit 201 formed by integrating a semiconductor laser, acollimator lens, etc. into a unit, a cylinder lens 202 converting alaser beam in the form of a parallel beam generated therefrom intoconvergent light in a sub-scanning direction, and a scanning unit 203for deflecting the laser beam emitted from the light source unit 201such that the laser beam scans the photosensitive drum 101. The scanningunit 203 has a polygonal mirror 204 a having a plurality of reflectionsurfaces for deflecting the laser beam, a drive motor (not shown) forthe polygonal mirror 204 a, a board 205, and an integrated circuit (IC)chip 206. The optical scanning apparatus 200 has a lens 207 effectingimage formation on the surface of the photosensitive drum 101 with thelaser beam that has been deflected by the polygonal mirror 204 a, and areflection mirror 208 guiding the laser beam to the photosensitive drum101. The components of the optical scanning apparatus 200 areaccommodated in an optical box 209.

The laser beam based on input image data is emitted from the lightsource unit 201. This laser beam passes through the collimator lens andthe cylinder lens 202, and then impinges upon one of the plurality ofreflection surfaces which the polygonal mirror 204 a being rotated has.Since the polygonal mirror 204 a is rotating, the laser beam is turnedinto scanning light after the reflection. After this, image formation iseffected on the photosensitive drum 101 by the lens 207. In FIG. 2,symbol L indicates the laser beam emitted from the light source unit201. In FIG. 2, symbol Ls indicates the path of the laser beam Lundergoing scanning by the polygonal mirror 204 a. In this way, anelectrostatic latent image is formed in the rotation axis direction(main scanning direction) of the photosensitive drum 101 through thescanning by the polygonal mirror 204 a, and an electrostatic latentimage is formed in sub-scanning direction through the rotation of thephotosensitive drum 101.

In an image forming apparatus equipped with the optical scanningapparatus 200, to reproduce a high definition image, it is beneficial toguide the laser beam onto the photosensitive drum 101 while minimizingdeviation of the optical path so that the laser beam from the lightsource unit 201 follows the desired optical path at the time ofdesigning. For this purpose, utmost caution is used in terms of thepositions and attitudes of the optical components when they are mounted.

Above all, the orientation of the rotation shaft of the polygonal mirror204 a influences the scanning line curving on the photosensitive drum101 and the beam spot diameter, so that, to maintain high image quality,it is necessary to adjust the inclination of the rotation shaft of thepolygonal mirror 204 a. For example, in the state in which the polygonalmirror 204 a is installed in the optical box 209, when the rotationshaft is inclined with respect to the predetermined angle at the time ofdesigning (hereinafter, this will be referred to as shaft inclination),the rotation shaft of the polygonal mirror 204 a does not allow theincident light to impinge upon a reflection surface thereof at apredetermined angle. Then, the optical path of the laser beam after thereflection may deviate from the predetermined optical path, so that theoptical path after the reflection deviates from the portion where theoptical performance of the lens 207 is high (i.e., from the portionwhere the performance as expected at the time of designing is exerted).As a result, the spot of the laser beam effecting image formation on thephotosensitive drum 101 is not of a desired size and shape. In view ofthis, it is necessary to adjust the orientation of the rotation shaft ofthe polygonal mirror 204 a such that no shaft inclination occurs wheninstalling the polygonal mirror 204 a (hereinafter, this adjustment willbe referred to as shaft inclination adjustment).

In the optical scanning apparatus according to the present exemplaryembodiment, it is possible to perform shaft inclination adjustment witha simple construction without involving an increase in apparatus size.In the following, the construction of the optical scanning apparatuswill be described in detail.

FIG. 3A illustrates how the scanning unit 203 is installed in theoptical scanning apparatus 200 according to the present exemplaryembodiment. The drive board 205 of the scanning unit 203 is providedwith a plurality of holes for passing screws for fixing the drive board205 to an installation portion 301 of the optical box 209. Adjustmentscrews 302 and 303 and fixation screws 304 and 305 are passed throughthese holes. Bearing surfaces 306, 307, 308, and 309 are provided so asto protrude from the installation portion 301 of the optical box 209.Female screws are formed in the interiors of the bearing surfaces. Byfastening the adjustment screws 302 and 303 and the fixation screws 304and 305 to the female screws, the drive board 205 is fixed to theinstallation portion 301. A bearing 208 for a rotation shaft 204 b ofthe polygonal mirror 204 a is fit-engaged with a fit-engagement holeprovided in the drive board 205 by swaging. Through the fit-engagementof the bearing 208 with the fit-engagement hole, the polygonal mirror204 a and the drive motor 204 c are fixed to the drive board 205. Thebearing 208 also serves as the positioning boss of the scanning unit203, and is fit-engaged with a positioning hole 312 provided in theoptical box 209, whereby positioning is effected on the scanning unit203 within the optical box 209.

As illustrated in FIG. 3A, when fixing the drive board 205 to theinstallation portion 301 of the optical box 209, the adjustment screw302 and the adjustment screw 303 are passed through the holes providedin the drive board 205. Further, O-rings 310 and 311 are providedbetween the drive board 205 and the installation portion 301. Theinstallation portion 301 is provided with the bearing surfaces 306 and307. The bearing member is provided with a counterbore (recessedportions, spot facing) for accommodating the O-rings 310 and 311. Theadjustment screws 306 and 307 are passed through the holes of theO-rings 310 and 311. The height of the O-rings is larger than the depthof the counterbore. Thus, by tightening the adjustment screws 302 and303, the O-rings 310 and 311 are pressurized by the drive board 205 andthe installation portion 301. As a result, a vertical reaction force isgenerated in the O-rings 310 and 311, and the drive board 205 is fixedto the installation portion 301 by the reaction force. Further, byadjusting the respective tightening amounts of the adjustment screws 302and 303, it is possible to vary the respective compression amounts(amounts of deformation) of the O-rings 310 and 311, so that it ispossible to arbitrarily vary the inclination (height) of the drive board205 with respect to the installation portion 301. When the inclinationof the drive board 205 is changed, the inclination of the rotation shaft204 b fit-engaged with (fixed to) the drive board 205 is also changed.Thus, by adjusting the tightening amounts of the adjustment screws 302and 303, it is possible to adjust the shaft inclination. The O-rings 310and 311 are configured such that the inner diameters thereof conform tothe nominal diameters (outer diameters) of the adjustment screws 302 and303.

As illustrated in FIG. 3A, the adjustment screws 302 and 303 arerespectively provided with plain washers 314 and 315 for preventingwarpage of the drive board 205 due to the deformation of the O-rings 310and 311. The outer diameter r of the plain washers 313 and 314illustrated in FIG. 3A is smaller than the inner diameter R of thebearing surfaces 306 and 307 (the diameter of the counterbore) butlarger than the diameter Or of the O-rings 310 and 311.

By crushing the O-rings 310 and 311, it is possible to adjust the heightof the drive board 205 with respect to the installation portion 301. Atthe time of adjustment, when the adjustment screws 302 and 303 aretightened, an appropriate reaction force is required within a range notcausing abnormal deformation of the O-rings 310 and 311. It is necessaryfor this nature not to undergo changes with passage of time. As amaterial having such a nature, a rubber member composed of syntheticrubber is excellent. Typical examples of such a material includematerials capable of elastic deformation, such as nitrile rubber,hydrogenated nitrile rubber, ethylene propylene rubber, silicone rubber,fluoro rubber, and acrylic rubber.

FIG. 3B is a plan view, as seen from the direction of the rotation shaft204 b of the polygonal mirror 204 a, of the drive board 205 installed onthe installation portion 301. In the optical scanning apparatus 200according to the present exemplary embodiment, the laser beam L impingesupon the polygonal mirror 204 a from the direction illustrated in FIG.3B to be turned into scanning light Ls. Further, as illustrated in FIG.3B, the adjustment screws 302 and 303 are arranged with respect to theposition of the rotation shaft 204 b such that a line segment connectingthe position of the adjustment screw 302 and the position of therotation shaft of the polygonal mirror and a line segment connecting theposition of the adjustment screw 303 and the position of the rotationshaft of the polygonal mirror are substantially orthogonal to eachother.

FIG. 4 illustrates how the shaft inclination value (the angulardeviation of the rotation shaft 204 b with respect to an axisperpendicular to a reference plane of the optical box 209) is changedwhen shaft inclination of the rotation shaft 204 b is adjusted byactually tightening the adjustment screws 302 and 303 provided at twopositions. The horizontal axis indicates the shaft inclination in theX-direction in FIG. 3B, and the vertical axis indicates the shaftinclination in the Y-direction, with an angle perpendicular to thereference plane of the optical box 209 serving as an origin. In FIG. 4,line (1) shows how the shaft inclination changes when the adjustmentscrew 302 is tightened while fixing the adjustment screw 303 inposition. Line (2) shows how the shaft inclination changes when theadjustment screw 302 is loosened while fixing the adjustment screw 303in position. Line (3) shows how the shaft inclination changes when theadjustment screw 303 is tightened while fixing the adjustment screw 302in position. Line (4) shows how the shaft inclination changes when theadjustment screw 303 is loosened while fixing the adjustment screw 302in position. The plots in FIG. 4 indicate how the shaft inclinationvalue changes when the adjustment screws 302 and 303 are turned by 90°.As illustrated in FIG. 4, the shaft inclination changes mainly in theY-direction according to the tightening amount of the adjustment screw303. With the adjustment screw 302, the shaft inclination changes mainlyin the X-direction. As illustrated in FIG. 3B, the adjustment screw 302and the adjustment screw 303 are arranged with respect to the positionof the rotation shaft 204 b such that the line segment connecting theadjustment screw 303, which is one adjustment screw, and the rotationshaft of the polygonal mirror, and the line segment connecting theadjustment screw 302, which is the other adjustment screw, and therotation shaft of the polygonal mirror, are substantially orthogonal toeach other. With this arrangement, it is possible to adjust theorientation of the rotation shaft 204 b in an arbitrary direction byadjusting the tightening amounts of the adjustment screws 302 and 303.Thus, no matter what way the inclination at the time of initial assemblymay be, the shaft inclination can be reliably adjusted from twodirections by adjusting the tightening amounts of the adjustment screws302 and 303. Assuming that the distance between the adjustment screw 302and the rotation shaft 204 b and the distance between the adjustmentscrew 303 and the rotation shaft 204 b are substantially equal to eachother, the rotation shaft 204 b undergoes a fluctuation in theinclination by substantially the same change amount by tightening theadjustment screws by the same tightening amount, which is convenient forthe operator or the adjustment apparatus, etc. In the present exemplaryembodiment, by adjusting the height of the drive board 205 by ±0.2 mm,it is possible to cancel shaft inclination caused by accumulation ofcomponent tolerances.

The O-rings 310 and 311 are compressed according to the tighteningamounts of the adjustment screws 302 and 303, and the drive board 205 ispressed against the adjustment screws 302 and 303 by the reaction forcethereof. In the following, the proper magnitude of the reaction forcewill be described. While in the related-art technique the drive board isfastened to the installation surface of the optical box totally byscrews, in the construction of the present exemplary embodiment, thereexists, as illustrated in FIG. 3, an adjustment portion where the driveboard is upwardly urged. Generally speaking, the high-speed rotationdrive motor used in the scanning unit 203 generates a large vibrationdepending upon the balance thereof, so that it is desirable for thedrive motor to be perfectly fixed to the member in which it isaccommodated by screw fastening. This is all the more so if exposure isto be effected through scanning with a laser beam by using the polygonalmirror 204 a. In the construction of the optical scanning apparatusaccording to the present exemplary embodiment illustrated in FIGS. 3Aand 3B, the drive board is not perfectly fixed to the installationsurface of the optical box, so that the effect of suppressing vibrationis reduced. However, it is advantageous in that it allows adjustment ofthe shaft inclination of the scanning unit 203. As described above, atthe above adjustment portions of the optical scanning apparatusaccording to the present exemplary embodiment, the drive board 205 isupwardly urged by the reaction force of the O-rings 310 and 311, and itis to be assumed that the magnitude of the reaction force of the O-rings310 and 311 influences the magnitude of the vibration of the scanningunit 203. In this connection, the graph of FIG. 5 illustrates therelationship between the reaction force of the O-rings and the magnitudeof the vibration. In the graph, the horizontal axis indicates thereaction force of the O-rings 310 and 311, and the vertical axisindicates the acceleration of the drive board 205, which is supposed torepresent the vibration level of the scanning unit. In the graph, thelong and short dash line indicates the vibration level when the driveboard is fastened to the installation surface of the optical boxcompletely by screws. In FIG. 5, the curve indicates the vibration levelin the present exemplary embodiment. As can be seen from FIG. 5, inorder for the vibration level of the drive board 205 in the presentexemplary embodiment to be equal to or less than the vibration level inthe case of screw fastening, it is necessary for the reaction force ofthe O-rings to be at least approximately 4 kgf to 5 kgf or more.Conversely, if a level where the reaction force is equal to or more thanthat is adopted, the vibration is not easily generated, and it ispossible to adjust shaft inclination. Thus, when adopting theconstruction of the present exemplary embodiment, the nominalcompression amount is to be set such that a reaction force ofapproximately 4 kgf to 5 kgf can be secured for the O-rings even in thecase of the maximum loosening amount imaginable for the adjustmentscrews 302 and 303.

For example, when O-rings of a length of 2.6 mm and an inner diameter of3.6 mm are adopted, it is possible to perform designing with an O-ringreaction force of 8 kgf when the nominal compression amount is 1 mm, andwith an O-ring reaction force of 5 kgf to 11 kgf, even if a change inthe compression amount of the O-rings due to the shaft inclinationadjustment is allowed for.

In contrast, when, as discussed in Japanese Patent Application Laid-OpenNo. 2005-201941, designing is performed so as to obtain a reaction forceof 8 kgf by using a compression spring as the elastic member, even ifthe spring constant is set high due to the reduction in the size of thecompression spring, the height in the free state of the compressionspring is 10 mm and the height thereof during operation is approximately8 mm, which means the size involved is approximately four times that inthe case of the construction employing O-rings. Further, since theheight in the free state of the elastic member is large, when assemblingthe scanning unit to the optical box, it is rather difficult to effectpositioning on the scanning unit, so that the assembly is ratherdifficult to perform.

Thus, the shaft inclination adjustment system using O-rings helps toachieve a reduction in size, and is superior to the elastic membercomposed of a compression spring, a plate spring or the like. The shaftinclination adjustment is performed as follows before factory shipmentor at the time of maintenance by a service engineer. The assembly workeror the service engineer arranges a jig in the optical path of a lightbeam, and detects the light beam reflected by the polygonal mirror 204 aby means of a charge-coupled device (CCD) provided in the jig. Then,looking at the position of the light beam incident on the CCD, theassembly worker or the service engineer determines the tighteningamounts of the adjustment screws 302 and 303.

A second exemplary embodiment of the present invention will be describedwith reference to FIGS. 6A through 6E and FIG. 7. The second exemplaryembodiment differs from the first exemplary embodiment in that thecounterbore provided with the bearing surfaces 306 and 307 are providedwith recessed portions for allowing deformation of the O-rings 310 and311. More specifically, a recessed portion 601 as illustrated in FIGS.6A, 6B, 6C, and 6D is provided in a part of the counterbore providedwith each of the bearing surfaces 306 and 307. Otherwise, the secondexemplary embodiment is of a construction the same as, or alternativelysimilar to, that of the first exemplary embodiment, so, in the followingdescription, the portions that are the same as, or alternatively similarto, those of the first exemplary embodiment are indicated by the samereference numerals as in the first exemplary embodiment.

FIGS. 6A, 6B, 6C, and 6D are schematic sectional views of the adjustmentscrew 302, the O-ring 310, and the bearing surface 306. FIGS. 6A, 6B,6C, and 6D illustrate how the O-ring undergoes deformation when theadjustment screw 302 is actually tightened to adjust shaft inclination.Here, what is characteristic is that the optical box 209 is providedwith a clearance configuration 601 conforming to the deformation of theO-ring due to the compression thereof. On the other hand, FIG. 6Eillustrates how the O-ring is compressed through tightening of theadjustment screw in a construction provided with no clearanceconfiguration. The constructions of the adjustment screw 303, the O-ring311, and the bearing surface 307 are similar to those of the adjustmentscrew 302, the O-ring 310, and the bearing surface 306.

By tightening the adjustment screw 302, the O-ring undergoes elasticdeformation so as to be shrunk in the direction of the rotation axis 204b and undergoes elastic deformation so as to expand in the radialdirection of the rotation shaft 204 b (i.e., along the surface of theboard). However, in the construction as illustrated in FIG. 6E, in whichthere is no escape for the deformed O-ring, the O-ring is stiffened, itspliability is reduced, so that the linearity of the reaction force isimpaired. Then, the tightening torque of the adjustment screw 302increases accordingly. If the adjustment screw is forcibly pushed in,due to the reduction in the elasticity of the O-ring, which has shrunkand stiffened, it is impossible to adjust the height of the drive board205 in conformity with the tightening amount. As a result, the precisionin the shaft inclination adjustment deteriorates. To prevent this, itmight be possible to secure a large escape in the radial direction ofthe rotation shaft 204 b. In that case, however, it would be necessaryto simultaneously enlarge the plain washer 313 for preventing the driveboard 205 from following the deformation of the O-ring, which meansthere would be a possibility of the plain washer interfering with acomponent on the drive board 205.

In view of this, there is provided in the bearing surface 306, 307 ofthe optical box a clearance configuration (recessed portion 601) forallowing deformation of the O-ring when the compression amount of theO-ring has increased to a certain degree as illustrated in FIGS. 6C and6D, that is, when the O-ring has greatly expanded in the radialdirection of the rotation shaft 204 b. Due to the provision of therecessed portion 601, the linearity of the O-ring reaction force ismaintained, and the height of the drive board 205 is adjusted inconformity with the tightening amount, and it is possible to perform theshaft inclination adjustment with high precision. By varying theconfiguration of the recessed portion 601, it is possible to design aprofile of an optimum spring constant. In the present exemplaryembodiment, an annular (circular) O-ring is used, so that the recessedportion 601 is provided so as to allow the O-ring, which is deformedradially around the rotation shaft 204 b, to undergo downwarddeformation as illustrated in FIG. 6D.

FIG. 7 is a graph illustrating, by way of example, the relationshipbetween the compression amount of the O-ring and the compression amountthereof. As can be seen from the graph, in the case where a clearanceconfiguration (recessed portion) is provided in the optical box, therelationship between the compression amount of the O-ring and thereaction force thereof is such as can be expressed in a neat linearline, which means resiliency is maintained. On the other hand, in a casewhere no recessed portion is provided as illustrated in FIG. 6E, aprofile in the form of a quadratic curve results as indicated by line(6) in FIG. 7, with the linearity of the reaction force being impaired.Thus, it is more desirable to provide the optical box with a clearanceconfiguration (recessed portion) allowing the deformed O-ring to escape.

In this way, by providing the recessed portion 601 in the bearingsurface in which the O-ring is accommodated, it is possible to adjustshaft inclination easily and with high precision even if the compressionamount of the O-ring is large.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures, and functions.

What is claimed is:
 1. An optical scanning apparatus comprising: apolygonal mirror configured to deflect a light beam emitted from a lightsource such that the light beam scans a member to be scanned; a drivemotor configured to rotate the polygonal mirror; a board on which thepolygonal mirror and the drive motor are mounted; a first installationportion and a second installation portion where the board is installedand a fixing portion where the board is fixed rigidly, wherein the firstinstallation portion and the second installation portion are arranged onsides opposite to each other across a first virtual plane connecting anoptical axis of the lens and a rotation shaft of the polygonal mirror,and the first installation portion and the second installation portionare arranged on a side opposite to the fixing portion with respect to asecond virtual plane intersecting the first virtual plane; a firstrubber member provided between the board and the first installationportion, wherein the first rubber member makes contact with the boardand the first installation portion; a second rubber member providedbetween the board and the second installation portion, wherein thesecond rubber member makes contact with the board and the secondinstallation portion; and a first screw configured to position the boardwith respect to the first installation portion and to deform the firstrubber member, wherein the first adjustment unit adjusts inclination ofthe board with respect to the first installation portion by deformingthe first rubber member; and a second screw configured to position theboard with respect to the second installation portion and to deform thesecond rubber member, wherein the second adjustment unit adjustsinclination of the board with respect to the second installation portionby deforming the second rubber member.
 2. The optical scanning apparatusaccording to claim 1, wherein the second virtual plane intersectsneither the first installation portion nor the second installationportion and does not pass between the first installation portion and thesecond installation portion.
 3. The optical scanning apparatus accordingto claim 1, further comprising: a lens on which the light beam deflectedby the polygon mirror is incident, wherein a distance from the lightbeam deflected by the polygon mirror to the first installation portionand the second installation in a scanning direction is shorter than alength of the lens in the scanning direction.
 4. An optical scanningapparatus comprising: a polygonal mirror configured to deflect a lightbeam emitted from a light source such that the light beam scans a memberto be scanned; a drive motor configured to rotate the polygonal mirror;a board on which the polygonal mirror and the drive motor are mounted; afirst installation portion and a second installation portion where theboard is installed and a fixing portion where the board is fixedrigidly, wherein the first installation portion and the secondinstallation portion are arranged on sides opposite to each other acrossa virtual plane connecting an optical axis of the lens and a rotationshaft of the polygonal mirror, and the first installation portion andthe second installation portion are arranged outside each end of ascanning area of the light beam deflected by the polygon mirror; a firstrubber member provided between the board and the first installationportion, wherein the first rubber member makes contact with the boardand the first installation portion; a second rubber member providedbetween the board and the second installation portion, wherein thesecond rubber member makes contact with the board and the secondinstallation portion; and a first screw configured to position the boardwith respect to the first installation portion and to deform the firstrubber member, wherein the first adjustment unit adjusts inclination ofthe board with respect to the first installation portion by deformingthe first rubber member; and a second screw configured to position theboard with respect to the second installation portion and to deform thesecond rubber member, wherein the second adjustment unit adjustsinclination of the board with respect to the second installation portionby deforming the second rubber member.
 5. The optical scanning apparatusaccording to claim 4, wherein the first installation portion and thesecond installation portion are arranged on a side opposite to thefixing portion with respect to another virtual plane intersecting thevirtual plane.
 6. The optical scanning apparatus according to claim 5,wherein the other virtual plane intersects neither the firstinstallation portion nor the second installation portion and does notpass between the first installation portion and the second installationportion.
 7. The optical scanning apparatus according to claim 4, furthercomprising: a lens on which the light beam deflected by the polygonmirror is incident, wherein a distance from the light beam deflected bythe polygon mirror to the first installation portion and the secondinstallation in a scanning direction is shorter than a length of thelens in the scanning direction.